1. Field of the Invention
The present invention relates to spectrometers and more particularly, to holographic spectrometers enabling the simultaneous determination of spatial and spectral information of a light source.
2. Description of Related Art
Holographic spectrometers are well known in the art and are used to determined spectral information from radiant sources. These spectrometers determine the spectral content of the light contained in the source. Generally, a spectrometer that is used to determine spectral information from a light source is shown in FIG. 1. The spectrometer of FIG. 1 illustrates a light source (1) radiating a beam (2) which is projected into a beam splitter (3). The radiant beam (2) is split into two beam components (4) and (5). The beam components (4) and (5) are projected towards mirrors (6) and (7). The beams (4) and (5) are reflected from one mirror to the other mirror, as shown by the arrows in the drawing, and are directed back towards the beam splitter (3). The beam splitter (3) projects the reflected beam components (4) and (5) through a lens (8) which, in turn, projects the beams onto an interference plane (9). As can be seen in the figure, mirror (6) is positioned a desired distance behind the symetrical mirror position indicated by dash line (10) and virtual sources (11) and (12) are formed behind the mirror (6). This positioning enables the two beam components (4) and (5) to interfere with one another, causing an interference pattern, directed by the lens (8), to be projected onto the interference plane (9) for determining spectral information of the source by the application of fourier transform techniques to the measured interference pattern of the two beam components. As the beam components are projected onto the interference plane, all spatial information about the source is lost. Only spectral information can be determined from the interference plane. This type of spectrometer only measures the spectral content of polychromatic extended scenes. Therefore, this art has the disadvantage that it can only determine spectral information.
Dispersive spectrometer may be used with a position encoding device to determine two-dimensional spatial positioning of a light source. However, since dispersive spectrometers only accept line fields of view, position encoding with a dispersive spectrometer requires complex fiber optic reformatting to accomplish the simultaneous determination of the two-dimensional spatial position and spectral content of the light source. The use of fiber optics with the dispersive spectrometer is not only complex but is very expensive.